A-LevelBiologySelection and evolution9700/42 · Feb/Mar 2021 · Q110 Marks

The European eel, Anguilla anguilla, is a fish. The sizes of eel populations tend to remain relatively stable despite eels producing large numbers of offspring.

(a)Suggest two reasons why the population sizes of eels tend to remain relatively stable.[2]
(b)Explain what is meant by the general theory of evolution.[2]
(c)The generation time of a species is the mean (average) time from one generation (parents) to the next generation (offspring). For example, the generation time of humans is about 25 years. Fig. 1.1 shows a graph of the relationship between the rate of evolution and the generation time for a wide range of different species. [Figure 1.1] Describe and explain the relationship shown in Fig. 1.1.[3]
(d)The tuatara, Sphenodon punctatus, is a reptile that is native to New Zealand. It is found nowhere else in the wild. Fig. 1.2 shows a tuatara. [Figure 1.2] Tuataras have a slow growth rate and can live for over one hundred years. Fossil evidence shows that there has been little morphological change in the tuatara over the last 200 million years. This is a much lower rate of evolution than would be expected from the generation time of this species. Suggest and explain why the tuatara has remained largely unchanged over the last 200 million years.[3]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2021). The mark or mark type is shown in brackets.

[1] predation / fishing;
[1] food qualified ; e.g. competition / limited amount
[1] disease;
[1] AVP; e.g. idea that birth rate and death rate are roughly equal
[1] organisms have changed over time ;
[1] ref. to natural selection / selective advantage for survival / survival of the fittest;
[1] ref. to long period of time;
[1] ref. to variation;
[1] as the generation time increases, the rate of evolution decreases / relationship is inversely proportional / AW ; ora
[1] not linear / exponential / decreasing gradient ;
[1] (longer generation time) so less, reproduction / DNA replication; ora
[1] ref. to fewer mutations; ora
[1] idea of (so) less chance of evolution ; ora mp5 must be linked to mp3 or mp4
[1] well adapted to their environment;
[1] environment/selection pressures, stayed, constant/stable ; ora
[1] mutations qualified ; e.g. fewer/not selected for/low rate
[1] AVP; e.g. no natural predators / cannot migrate / no separation of populations (for speciation to occur)

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